Wave modulating



Nov. 8, l 92 7.

J. F. FARRINGTON WAVE MODULATIHG Filed July 51, 1920 Fig. 5.

n a. m. mm .A J m Patented Nov. 8, 1927.

UNITED srras earanroricn.

J OHN F. FARRINGTOIN', 01F YORK, N. Y., ASSIGNOR TO WESTERN ELECTRIC COMI- rAnY, INCORPORATED, on NEW roan,

N. Y., A GGBPOEATION OF NEW YORK.

WAVE :MODULATI'NG.

Application filed JuIy 31,

. This invention relates to modulating systems and circuits for use in signaling or other wave transmission systems, and, more particularly, in telephone systems; a

5 An object of the invention is to provide improvements insystems and methods of modulation dependent upon the principle of variable absorption of the high frequency energy.

The herein described systems embodying the invention comprise space discharged oscillators having a suitable current supply circuit, an input circuit connected to a cathode and the grid or other equivalent eler ment of the device, and an output circuit connected to the cathode and the anode. In

shunt to the output circuit is the primary of a high frequency transformer whose secondary is connected to. a variable impedance modulating device of any suitable type, but preferably, a discharge tube having its input circuit controlled by the source of waves or signals, in. accordance with which the modulation is to be eil eeted. This type of modulator acts to cause variable generation of waves by the oscillator. The absorption device causes a large ellfect since at, those instances when maximum high frequency energy is being absorbed in the modulator, minimum high frequency energ is being supplied to the grid circuit of the oscillator, and vice versa. But certain principles oi? the invention may be applied in systems in which there is substituted. for the oscillator, a device having a separate source of high frequency waves applied to the input circuit thereof.

The aims and objects of the invention will be more thoroughly understood by references to the following description and the appended claims. Tn the accompanying drawing Figs. 1 and. 2 represent the application ofthe invention in systems employing different forms of oscillators, while '3 rep- CAD to resents an auto-transformer which may be substituted for the transformer 9, 10 of Figs. 1 and 2. i

In Fig. 1a tube or. system of tubes 1 of the ordinary type comprising a heated filamcntarycathode, and anode and an impedance controlling grid containedv in a highly evacuated vessel, is connected to an antenna circuit 2 for the generation 01": oscillations at therein. The high frequency output circuit 1920. Serial No. 400,363.

between the anode and. the cathode is connected across theradiating capacity of the antenna circuit. The input circuit between the cathode and the grid is connected across the capacity? For convenienceof adjustment it may be also connected across a small portion of the inductance of the antenna circuit. A. uitable source 4 supplies space current between the anode and the cathode. lf the source 4 is of material. impedance to waves of the frequency to be generated by the oscillator, capacity 5 may be pro vided to furnish a low impedance path therearound. The tuning oi the antenna may be varied in any convenient mannerto change the trequenc 1 of the waves produced. Auxili elements of the oscillator which aid in producing etlicient operation, are a condenser 6 in the grid circuit and a high'resistance leal: path 7 connected between the grid and the-filament. so far described, the sys tem is incapable of generating oscillations since the circuit 8' through the source a would constitute a short circuit upon the output circuit of. the oscillator if no impedance elements were connected therein. This is prevented from acting as a short circuit, by including the primary 9 of a transformer therein. The secondary 10 of the trans iormer included in the'plate circuit of a variable impedance tube 11, which is con trolled by a source of speech or other signal waves, such microphone circuit 12 connected to the input circuit 13 thereof. It the secondary 10 were removed from. the system, primary 9 would act as a choke coil to prevent the passage of high frequency Iivaves through circuit 8.

The same result will occur if the secondary 10 is included in a circuit of very high impedance. In practice. however, the impedance of the circuit including the secondary 10 is adjusted by varying the batteries-1 and 15 so that the amount of energy absorbed in the device 11- will bring the waves generated by the device 1 to the desired average value. The sound frequency waves acting in the microphone circuit 12 will. cause the impedance of the device 11 to vary, thereby varying the energy transferred from the primary 9 to the secondary 10, and causing corresponding variations in the high frequency waves produced in and radiated from the antenna circuit 2.

he transformer 9, 10 is preferably, in the case of radio systems, designed to elliciently transfer energy corresponding in frequency to that desired to be radiated. 'llhe coupling between the primary and the secondary may be made variable in any convenient manner. A tight coupling with small capacity between the primary and sec-- ondary is usually desirable. While magnetic material may be used for the case of this transformer in some instances it should be clearly understood that, in accordance with this invention, the transformer is always designed to transfer carrier or high frequency energy and not to transfer speech or low frequency energy. The batteries Li and 15 are not essential and either one or both of them may be omitted from the system but l ss distortion and greater ease of adjustment is realized when they are included.

in 2, a different form of oscillator is illustrateil in which the antenna circuit 2is insulated from the remainder of the system. The antenna circuit in this system likewise primarily determines the frcruiency of the generated oscillations which may lie-varied by varying the constants thereof; The transfer of high frequency energy to the antenna is accomplished through the coupling be tween the coils l6 and 17. The antenna circuit is connected back to the grid circuit of the tube through the coupling between the coils l8 and 19. A variable condenser 20 is connected in shunt to the coil 16. This condenser is made variable, not primarily for the purpose ofvarying the generated frequency, but for the purpose of changing the effective coupling of the anode-cathode circuit of the tube to the antenna and also for the purpose of preventing the occurrence of parasitic oscillations of undesiredfrequency in the system. The condenser 6 and resistance 7, while differently located, function in a manner similar to the correspondingly numbered elements in l igurel. In series with the source f is pl aced' an inductance coil 21 so designed as to prevent the passage-of current variations of speech frequency. Condenser 5 serves to bypass high frequency variations around the coil 21, although the distributed capacity of the coil 21 may be sufficient to render this by-pass unnecessary. The transformer primary 9 is connected in shunt to the capacity 20 and is associated with the secondary 10 and the elements 11, l2. l3, l4; and 15 inthe same manner as described in connection with Figure 1'.

In Figure 8 is illustrated an auto-transformer in which the windings 9 and 10 are consolidated. This may be substituted for that shown in the other figures.

In the operation ofthe systems described, high frequency waves produced in the an tenna circuit 2 will be caused tovary in amplitude in accordance with speech frequency variations in the circuit 12. if the wave length, the couplings of the oscillator with the antenna circuit, the constants of the modulating tube 11, and the transformer 9, 10 are properly tltljllf: ed for ellicient operation, then without change of the modulator 11 or the t'anshnrmer 9, 10, the system will w rlz eliiciently over a considerable range of adjustment of the oscillator and of the antenna for changing the wave length, or over a considerable "ange of variation of antenna constants, the: wave length. remaining-fixed. l urthermore, it is not necessary, if the transformer 9, 10, be suitably designed and adjusted that the impedance of the modulating tube 11 be extremely low. It is not convenient to provide tubes which will be of extremely low impedance without impressing a high positive potential upon the grid which would tend to cause distortion. Large amounts of power can therefore, by the use of transformers, le controlled without making the grid of the tube 11 excessively positive with respect to the cathode or without making it at all positive if a suitable negative grid battery 14; is used. Large amounts of power can be varied by a variable impedance of comparatively small power capacity.

ln applying the invention to transmistion over conductor lines a suitable closed nonradiating circuit'may be substituted for the antenna circuit 2 and a transmission line connected thereto in any desired manner. Variations of line or antenna constants n this case will not cause variations in carrier frequency. The *arricr waves generated. while referred to as high frequency waves. may in the caseof line transmission, be of a comparatively low frequency. This is particularly the case where the modulating waves are of relatively low frequency with respect to the essential frequencies of sound waves of speech. in any case the transformer 9, 10 will be modified to handle eiliciently energy of the frequency or frequencies to be transmitted. It should be understood, however that while the invention is applicable to other systems, it is more particularly designed for and usable in radio systems.

The novel features inherent in the invention are defined in the appended claims.

What is claimed is:

l. A. modulating system comprising an electron discharge device, appropriate circuits connected thereto whereby said device functions as a generator of carrier waves, said circuits including a grid-cathode circuit and an external anode-cathode circuit having a portion independent of said gridcathode circuit, and a modulating device including means for variably absorbing carrier wave frequency energy connected. in

inc

effective shunt to said independent portion of the external anode-cathode circuit.

2. A modulating system comprising an electron discharge device, appropriate circuits connected thereto whereby said device functions as a generator of carrier waves, said circuits including a grid-filament path and an anode-cathode path in addition to said grid-filament path, a modulating device including means for variably absorbing carrier frequency energy connected in high frequency energy shunt relation to said anodecathode path, and means for varying the impedance of said device in accordance with signals.

3. A modulating system comprises a space discharge device, appropriate circuits connected thereto whereby said device functions as a generator of carrier waves, said circuits including a cathode-anode circuit having a cathode-anode path within said device, a primary Winding of a transformer adapted to transfer carrier wave frequency energy connected across cathode-anode path, and a device variably absorptive of carrier wave energy in circuit with the secondary winding of said transformer.

, 4. A modulating system comprising a space discharge device, appropriate circuits connected thereto whereby said device functions as a generator of carrier waves, said circuits including a carrier wave output circuit, a transformer adapted to transfer carrier wave energy, the primary of said transformer being connected in shunt to a portion of said carrier wave output. circuit, and a modulating device variably absorptive of carrier wave energy connected in circuit with the secondary of said transformer.

5. A modulating system comprising an electron discharge device, appropriate circuits connected thereto whereby said device functions as a generator of high frequency oscillations,said circuits including a high frequency output circuit, a primary winding of a transformer adapted to transfer high frequency wave energy, connected in shunt to at least a portion of said output circuit, a space discharge tube in circuit with the secondary winding of said transformer, and means for varying the impedance of said tube in accordance with sound waves.

6. A modulating system comprising an electron discharge device, an input circuit for said device for receiving high frequency waves to be applied thereto, an output circuit for said device, a high frequency transformer having its primary winding connected across a portion of said output circuit, and a modulating discharge device of variable impedance to high frequency waves for variably absorbing the energy of such waves connected across the secondary winding of said transformer.

7 A modulating system comprising a space discharge device connectediwith appropriate circuits for the generation of high frequency oscillations, an output circuit for said device, a primary of a transformer adapted to transfer high frequency energy in shunt to said outputcircuit, and a modulating vacuum tube variably absorptiveof high frequency energy included in circuit with the secondary of said transformer.

8. A modulating system comprising a space discharge device, appropriate circuit arrangement connected thereto whereby said device functions as a generator of oscillations of carrier frequency, said circuits including an input circuit and an output circuit, a transformer adapted for the efiicient transfer of carrier frequency energy having its primary connected in shunt to one of said circuits, and a discharge device of variable impedance to high frequency energy connected in circuit with secondary of said transformer.

9. A modulating system comprising a space discharge device, circuit arrangements connected thereto for the generation of carrier oscillations, an output circuit for said device, a modulating device of variable impedance to the carrier oscillations, and means including a transformer eflicient for carrier wave frequencies connecting said modulating device to said output circuit whereby the carrier frequency potential difference applied to said modulating device bears a substantially constant relation to the carrier frequency potential difference across said output circuit irrespective of the adjustment of said circuit arrangements.

In witness whereof, I hereunto subscribe my name this 27th day of July, A. D. 1920.

JOHN F. FARRINGTON. 

